AU4147899A

AU4147899A - Rotary furnace with tubular central flow

Info

Publication number: AU4147899A
Application number: AU41478/99A
Authority: AU
Inventors: Christian Dreyer; Jean-Christophe Rotger
Original assignee: Aluminium Pechiney SA
Current assignee: Rio Tinto France SAS
Priority date: 1998-06-11
Filing date: 1999-06-08
Publication date: 1999-12-30
Anticipated expiration: 2019-06-08
Also published as: GC0000056A; DE69906296T2; NO322639B1; EP1093560A1; US6027339A; AU745152C; CA2334994A1; ZA200007066B; EG21714A; CN100445680C; NZ508349A; CA2334994C; FR2779811B1; TW432194B; ES2191433T3; CN1305579A; NO20006234D0; WO1999064804A1; AU745152B2; FR2779811A1

Description

RING FURNACE WITH CENTRAL TUBULAR FLOW Field of the invention This invention relates to ring furnace sections used for baking carbonaceous blocks, and particularly to furnaces with open type sections. 5 State of the art Ring furnaces with open type sections are known in themselves and have been described particularly in patent applications FR 2 600 152 (corresponding to 10 American patent US 4 859 175) and WO 91/19147. In these furnaces, a gas flow composed of air and/or combustion gases circulates through a series of active sections along the longitudinal direction of the furnace, inside a series of hollow heating walls (flue 15 walls) that communicate with one another between adjacent sections, each section being made up by alternately placing these heating walls,. in the transverse direction, adjacent to pits in which stacks of carbonaceous blocks to be baked are placed. This 20 gas flow is forced on the upstream of the active sections and is sucked up on the downstream side of these sections.

2 A hollow wall of a section is typically in the form of a rectangular parallelepiped 5 m long (in the longitudinal direction of the furnace), 5 m high and 0.5 m wide (in the transverse direction of the 5 furnace), that is a 0.3 m wide gas stream and twice a partition thickness of 0.1 m, subdivided into four vertical "shafts" by three vertical baffles placed in the transverse direction, each shaft being delimited either by two baffles, or by one baffle and one of the 10 walls of the section, in order to lengthen the average path taken by cooling air or combustion gases in the said wall and also to provide a constant spacing between the longitudinal partitions (side members) of the wall. 15 Apart from the baffles, tie bricks are also laid out in the transverse direction, particularly between the said baffles, in order to maintain a constant spacing between the longitudinal partitions of the wall. 20 Statement of the problem A continuous concern for a manufacturer of baked carbonaceous blocks is to reduce the production costs of these baked carbonaceous blocks, and investment 25 and/or maintenance costs of the furnaces used for their manufacture, particularly by extending the life of furnace refractory components, while maintaining constant quality. Another concern is to improve the quality of baked 30 carbonaceous blocks, and particularly to make the quality more constant and performances more uniform for a given carbonaceous block, and for different blocks.

3 Consequently, the applicant had the idea of modeling the circulation of gaseous fluids in existing furnace walls, knowing the dimensions and locations of baffles and tie bricks. 5 Firstly, he was surprised to find that the distribution of gas flows in hollow walls made according to the state of the art was far from being uniform and homogenous, such that under steady state conditions most of the gas flow traveled along 10 preferred paths, leaving a non-negligible part of the partitions of the wall without any contact with the said gas flow. However, these partitions separate the carbonaceous blocks in the pits from the said heating or cooling gas flows and provide heat exchange between 15 the gas flows and carbonaceous blocks. It is then more easily understood that this thermal heterogeneity of the partitions will either be the cause of variable quality in the carbonaceous blocks, or will necessitate (which takes place in practice) an increase in the 20 heating or cooling power such that even the blocks in the worst position for heat exchange will satisfy the specified quality requirements. Furthermore, the modeling also brought to light the large pressure loss in the gas flow due to the presence 25 of the baffles, which has two consequences; firstly it increases the energy necessary to make the gas flow circulate through the series of walls, and secondly it increases the corresponding overpressure or negative pressure in the said walls, which causes an increase in 30 thermal leaks inwards or outwards (from the said wall to the outside or from the outside to the said wall) and therefore the consumed energy.

4 Furthermore, since large temperature variations are frequently applied to the walls causing deterioration even though they are made of refractory bricks, they must be periodically replaced. Therefore the applicant 5 also looked for methods of making a more economic furnace, both in terms of operating costs and in maintenance and investment costs. Finally, they attempted to design methods of solving these problems (heterogeneous gas flow 10 distribution within the walls, etc.), not only to design new furnaces without the disadvantages of known furnaces, but also and especially so that existing old furnaces can be adapted and modified to produce more economic furnaces, in terms of operating costs and 15 maintenance costs. Considering the validity of the modeling recognized by the applicant, and the difficulty and very high cost of carrying out any experiments with real furnaces, the applicant searched for a solution to the problem caused using the same 20 modeling instruments that were used to isolate the cause of the problems to be solved. Description of the invention According to the invention, the ring furnace with 25 open type sections (open ring furnace) for baking carbonaceous blocks in a rotating fire comprises, along the longitudinal X direction of the furnace, a series of sections separated by headwalls provided with openings, each section comprising, along the transverse 30 Y direction of the furnace, hollow walls through which a heating gas flow comprising combustion gas or a cooling air flow circulates, alternating with pits containing carbonaceous blocks to be baked, each of the 5 said hollow walls in a section being in communication with a wall in an upstream section and/or a wall in a downstream section, so as to form a conduit through which the said gas flow circulates from the upstream 5 side to the downstream side in the X longitudinal direction on all sections fired simultaneously in the said ring furnace, each of the said walls of a section comprising two vertical lateral partitions in the X-Z plane, and elements in the transverse Y direction for 10 deflecting the said gas flow passing through the said wall and maintaining a constant spacing between the said lateral partitions, and is characterized in that each wall comprises a means of maintaining, over a length L' equal to at least one third of the length L 15 of the said wall, and typically by an appropriate choice of the said elements causing the said deflection, a gas flow of rate D uniformly distributed over the entire normal cross-section S of the said wall in the Y-Z plane, with uniformity of the said flow 20 distribution of the flow rate D defined by the expression "2 y D - 0.5 y D / y S", where "2 y D - 0.5 y D" denotes the extent of the range of the flow D corresponding to a fraction y of the said normal cross section S, and in which y is a the most equal to 0.25. 25 The invention is distinguished from state-of-the art furnaces in that the vertical baffles, usually three for each hollow wall, are eliminated. According to the state of the art, if L denotes the length of the hollow wall in the X direction, H its 30 height in the Z direction and as a first approximation if the height C of the baffles in the Z direction is assumed to be equal to the height M of the- headwalls at the ends of the said wall, the average path of the gas 6 flow may be broken down into a component along the longitudinal X direction over a length L, and a component in the vertical Z direction over a length 4xC, giving a total of L + 4xC. 5 The values of C and M are typically between 0.6xH and 0.8xH. Thus with 3 baffles, the gas flow is a tubular flow that changes direction 8 times (X/Z-X/Z X/Z-X/X), each baffle creating a direction change in the vertical direction Z and in the longitudinal 10 direction X denoted "Z-X", by alternating longitudinal directions (X) and vertical directions (Z), the entire gas flow being concentrated at each passage through a baffle, over a normal cross-section S corresponding to a height of 0.2xH - 0.4xH, in other words 20 to 40% of 15 the entire cross-section S. However according to the invention, and in the case in which the same type of hollow wall is used, the average gas flow goes along an average path which, as a first approximation and considering the lack of 20 vertical baffles, is equal to the arithmetic mean of the shortest path (the length L) and the longest path (the length equal to L + 2xM), in other words -(L + L + 2xM) or L+M, to be compared with the path according to the state of the art which is equal to L + 4xC, where C 25 is close to M. Furthermore, due to an appropriate choice of the said elements controlling the said deflection, the gas flow, of rate D, is typically uniformly distributed over the entire normal cross-section S of the said wall 30 in the Y-Z plane, with a degree of homogeneity of the said distribution of the flow rate D equal to 0.50 D 0.125 D/0.25 S, the said degree of homogeneity being denoted "2 y D - 0.5 y D / y S", where "2 y D - 0.5 y 7 D" is the extent of the fraction of the flow rate D corresponding to a fraction y (where y is not more than 0.25) of the said normal cross-section S which is equal to the product of the height "H" by the constant width 5 "1" of the hollow walls. Considering the fact that the deflection elements are oriented in the transverse direction Y and the resulting symmetry, the formula giving the degree of homogeneity is also valid in the X-Z plane, the cross 10 section S then being replaced by the height "H" where y is a fraction of this height H. Since the normal cross-section S is always taken in the Y-Z plane and the elements controlling the deflection being in the transverse Y direction, a 15 digital simulation can be used to represent the distribution of the flow rate D in the X-Z plane of a hollow wall, as shown in Figures 3 and 4 representing sections or cross-sections through furnaces or hollow walls in the X-Z plane. 20 Gas flows are modeled by breaking down the total gas flow into a number N of elementary gas streams for example about fifty streams as shown in Figures 3 and 4, and it displays the trajectories of each of these streams in the X-Z plane and therefore the 25 distribution of elementary gas streams, in the same way as the spacing between contours on a map. Starting from this point, it is easy to calculate the real degree of homogeneity on each fraction "y" of the height H by counting the number "n" of elementary 30 streams necessary to obtain the fraction n/N corresponding to the fraction "y" of the height which was set equal to 0.25.

8 This choice of 0.25 and the corresponding expression for the degree of homogeneity represents the degree of homogeneity found necessary according to the invention to obtain the advantages of the invention. 5 Considering the law of mean, it is obvious that if the value of "y" increases, the degree of homogeneity is lower and is easier to achieve. Thus, the level expressed by "0.8 D - 0.2 D / 0.4 S" corresponds to a lower degree of homogeneity than that expressed by "0.5 10 D - 0.125 D / 0.25 S", to the extent that when the "y" fraction increases, the probability of a flow similar to yD also increases, by definition the entire flow D being present when y = 1. Conversely, the degree of homogeneity would strongly increase for a degree of 15 homogeneity such as "0.20 D - 0.05 D / 0.10 S", in which "y" is low, this degree of homogeneity not necessarily being accessible over a large portion with length L', and not necessarily compulsory to obtain a significant improvement in the advantages according to 20 the invention. Therefore, the global degree of homogeneity is in fact expressed as the portion of the surface of the hollow wall in the X-Z plane (or the corresponding volume) in which the degree of homogeneity reaches at 25 least a given threshold set equal to 0.5 D - 0.125 D / 0.25 S. According to the invention, at least the said degree of homogeneity is reached over at least one third of this area or (which is equivalent) one third 30 of the length L of the said hollow wall. The means according to the invention can solve the stated problem. Firstly, the invention gives a better distribution of the gas flow and therefore a better 9 temperature homogeneity while reducing the pressure loss, which actually leads to a more homogenous production, a reduction in furnace operating costs and longer life of the furnaces. 5 Description of the figures Figures 1, la, 2, 3 and 3a are applicable to furnaces according to the state of the art. Figures 4, 4a, 5, 6, 6a, 7a to 7d and 8 are applicable to furnaces 10 according to the invention. Figure 1 shows a diagrammatic sectional view along the X-Z plane, where X is the longitudinal direction and Z is the vertical direction, of the portion of the ring furnace 1 active simultaneously on 10 sections 2, 15 each section being separated from the next section by a headwall 32 provided with an opening 320 through which gas flows circulate with a flow rate D from the upstream side (at the right in the figure) where air is injected through a blowing ramp 231 fitted with one 20 pipe 230 for each longitudinal hollow wall 3 fitted with baffles 31 (three baffles per hollow wall and per section), towards the downstream side (at the left in the figure) in which the gas flow is suck up by means of an exhaust ramp 211 fitted with one exhaust ramp 210 25 for each longitudinal hollow wall. Burners 220 placed approximately in the middle of the series of the 10 sections, increase the temperature of the upstream gas flow to the required temperature, typically of the order of 11000C. The sections on the 30 upstream side of the burners are cooling sections for the carbonaceous blocks, while the sections on the downstream side of the burners are baking sections for the carbonaceous blocks.

10 Considering the pressure in the furnace, as shown in Figure la, a gas flow 233 can come out of the furnace on the upstream side of the burners, and a gas air flow 213 can penetrate into the furnace on the 5 downstream side of the burners. Thus, the gas flow of rate D circulating in the said hollow walls is not a flow of constant rate due to these gas flows 213, 233 and also to the formation of volatile products that can burn while the carbonaceous blocks are being baked in 10 the sections in the downstream part of the furnace. The gas flow is an air flow 34 in the upstream side of the burners 220, and is a combustion gas flow 35 mixed with an incident air flow 213 in the downstream part of the furnace, the rate of these flows being generically 15 denoted by "D". Figure la shows the pressure curve for the said gas flow of rate D inside the said hollow walls 3. The pressure decreases uniformly from the upstream side towards the downstream side; it is greater than 20 atmospheric pressure and maximum where air is blown into the ramp 230, it is close to atmospheric pressure immediately on the upstream side of the burners 220 where a pressure sensor 234 is installed, and is less than atmospheric pressure and minimum where the 25 combustion gases are induced into the exhaust ramp 210. Figure 2 shows a partially exploded perspective view of the upstream part of the series of active sections that shows, in the transverse direction Y for a given section 2, the alternation of hollow heating 30 walls 3 and pits 4 containing stacks of carbonaceous blocks 40. Each hollow wall 3 is limited in the X-Z plane -by two vertical partitions 38 and contains three baffles 31, is provided with peepholes 30 through which 11 a blowing ramp 230 can be inserted as shown in the figure, or exhaust ramp 210, burner injectors 220 or various measurement means. There are shafts 38 adjacent to the peepholes 30, in other words the space inside 5 the said wall without any obstacles in which the above mentioned devices can be placed (for example a blowing ramp) . The successive sections 2, two of which are shown in the figure, are separated by a wall 32 in which openings 320 are provided at the said hollow 10 walls 3 through which the gas flow can pass from the upstream to the downstream sides in the X'-X direction. Figure 3 shows a map of the gas flow obtained by digital simulation broken down into fifty elementary streams 6 in a hollow wall according to the state of 15 the art shown in Figure 3a, provided with 3 baffles 31 and a number of tie bricks 33 maintaining constant spacing between the partitions 38 of the said wall. The length L and the height H of a hollow wall for a given section, the height C of a baffle, the height M 20 of the wall 32 at both ends, are shown in Figure 3a. Figures 4 and 4a are similar to Figures 3 and 3a but are related to the invention. It is easy to see in Figure 4 that the degree of homogeneity defined by 0.50 D - 0.125 D / 0.25 S is achieved over the length L' 25 between abscissas X 1 and X 2 . The following can be seen in Figure 4, in which the gas flow circulates from the left to the right: - a first part denoted A, with length less than L/2 and preferably less than L/3, comprising means 30 (particularly tie bricks) of transforming an initial flow with the cross-section So into a flow with a .cross-section S extending over the entire hollow cross-section and with the said degree of 12 homogeneity, due to the formation of about ten flow fractions 7); - a second portion denoted B, with length equal to at least L/3 and preferably at least L/2, in which the 5 said degree of homogeneity is achieved everywhere; - a third portion denoted C, with the shortest possible length in which the gas flow is concentrated again, the said degree of homogeneity not being achieved since there may be local flow concentrations outside 10 the range 0.50D and 0.125D for a fraction of the cross-section equal to 0.25S. Figure 5 shows a second embodiment of the invention in a partial diagrammatic sectional view in the X-Z plane showing the gas flow on the same series of hollow 15 walls of sections simultaneously active for the same rotating fire, in the case in which the sections are not separated by headwall. The gas flow keeps approximately the same cross-section S over its entire path, a distribution means 232 being used on the 20 upstream side of the said rotating fire in order to inject a gas flow through transverse slits or openings 2320 in the form of about ten flow fractions 7 with the said degree of homogeneity, another distribution means 212 being used on the downstream side of the said 25 rotating fire in order to suck up the said gas flow through transverse slits or openings 2120 without affecting the said degree of homogeneity. Only the gas flows in the hollow walls at the two ends have been shown. The gas flow is composed of a set of flow 30 fractions 7 forming a tubular flow 50 located approximately along the longitudinal axis X'-X. .Figure 6 corresponds to figure 1 after modification according to Figure 5, particularly to eliminate the 13 headwalls 32 and after inserting distribution means 212, 232. This figure does not show means of providing homogenous heating of the said gas flow at the burners 220. Figure 6a corresponds to figure la, and shows the 5 static pressure curve for the said gas flow in a furnace according to the state of the art (curve I), and in a furnace according to the invention (curves II and III), curve II corresponding to the case in which the sections are separated by headwalls 32 with an 10 orifice 320 through which the gas flow passes, whereas curve III corresponds to the case shown in Figures 5 and 6 in which the gas flow maintains approximately the same cross-section S from upstream to downstream. Figures 7a to 7d are sections in the X-Z plane 15 illustrating tie bricks or elements that deflect the said gas flow, or gas streams 6 that flow around the said tie bricks 33a, 33b, 33c, 33d, some 33c and 33d having an oblong shape with a major axis 330 to facilitate the gas flow and to reduce its pressure loss 20 (loss of head). Figure 8 illustrates the case in which oblong shaped elements 33c, 33d are used and oriented such that the orientation of the major axis 330 of the said tie bricks coincides with the direction of the gas flow 25 in order to further reduce the pressure loss, particularly in the case in which the said sections are separated by walls 32 in which orifices or openings 320 are formed through which the said gas flow can pass from one section to the next. 30 Detailed description of the invention According to a first embodiment of the invention illustrated particularly in Figures 4 and 4a, the said 14 furnace 1 comprises sections separated by a headwall 32 with openings with cross-section So 320 through which the said gas flow 34, 35 passes from one wall to the next, and in which the said wall comprises a means in 5 its upstream part to create a flow with a cross-section S > So, starting from an initial flow of rate D at cross-section So, with the said degree of homogeneity equal to at least 0.50 D - 0.125 D / 0.25 S. In this embodiment, the cross-section of the said conduit 5 is 10 not constant, its cross-section being equal to So at each headwall 32 and S >> So in each hollow wall. Over a distance less than L/2, where L is the length of the said wall, the said means transforms a gas flow D with an initial cross-section So at the 15 entry upstream from the said wall, into a flow with a cross-section S equal to at least 3.So, and with the said degree of homogeneity. Preferably, the said distance is less than L/3. In Figure 4, the said means is located on the part denoted "A". 20 Each wall may comprise one or several peepholes 30 in its upper part which may be closed by a cover 36 that provide(s) access to shafts 37. According to the invention, the said means of achieving the said gas flow of rate D and cross-section 25 S with the said degree of homogeneity consists of divider elements, or tie bricks 33, dividing the said initial flow with cross-section So into about ten flow fractions 7, in a number of steps varying from 2 to 4 as shown in Figures 4 and 4a. Figure 4a shows three 30 steps as an example, that could be used to divide the initial flow So: the first comprising 2 tie bricks or elements 330, the second comprising 6 tie bricks or elements 331, and the third comprising 10 tie bricks or 15 elements 332, these 10 tie bricks or elements forming a front, the said degree of homogeneity being achieved on the downstream side of this front (at the right in Figure 4a). The initial flow So is thus divided into 11 5 flow fractions 7 over the entire cross-section S. According to another embodiment of the invention as shown in Figures 5 and 6, the cross-section of the said conduit 5 is constant, the said walls 32 having openings 320 with approximately the said cross-section 10 S in the Y-Z plane, in order to form conduits 5 with an approximately constant cross-section S from the upstream to the downstream sides, over all hollow walls 3 simultaneously active for the said fire, in which the said degree of homogeneity is achieved by means of a 15 removable distribution means 232 inserted on the upstream side of the said rotating fire, at the upstream end of the said conduit 5 in order to inject the said gas flow with the said degree of homogeneity into each conduit 5, in the form of about ten flow 20 fractions 7 - 8 fractions are shown in figure 5. Furthermore, in order to maintain the said degree of homogeneity over the longest possible length of the conduit 5, it may be advantageous to use a removable distribution means 212 also on the downstream side of 25 the said rotating fire, at the downstream end of the said conduit 5 formed by the series of hollow walls 3 active for the said fire, in order to induce the said gas flow without disturbing the said degree of homogeneity of the said gas flow on the upstream side. 30 According to the invention, the said distribution means 212, 232 may be a containment or a parallelepiped shaped distribution panel 232 with a plane horizontal cross-section in the X-Y plane, chosen such that the 16 said containment may be inserted vertically into the said shaft 37 in the said wall 3 or between two sections, or it may have a plane cross-section in the Y-Z plane slightly smaller than the said cross-section 5 S of the said wall in the Y-Z plane, with a face parallel to the Y-Z plane provided with openings 2320 with a geometry calculated either to inject the said gas flow in the form of flow fractions 7 with the said degree of homogeneity on the upstream side of the said 10 conduit 5, or to suck up the said gas flow on the downstream side of the said conduit 5. Regardless of the embodiment of the invention, the said means of maintaining a gas flow of rate D with the said degree of homogeneity over the said cross-section 15 S comprises a plurality of elements or tie bricks 33 fixed to the said lateral partitions 38 and distributed approximately uniformly along the surface of the said lateral partitions 38 in the X-Z plane of the said wall or the said conduit, depending on the results of the 20 digital simulation, with a sufficient number to ensure the said constant spacing between the said lateral partitions 38, so as to divide the said gas flow into a number of flow fractions 7 varying from 3 to 20 and uniformly distributed over the said entire cross 25 section S, and for the said fractions to produce a flow with a predetermined orientation, possibly along the said longitudinal direction X of the furnace, in order to give an approximately tubular flow 50 over all or part of the conduit 5 depending on the embodiment of 30 the invention. According to the first embodiment of the invention illustrated in Figure 4, about ten' flow fractions 7 are observed over the entire cross-section S in the part 17 denoted "B" with length L' over which the said degree of homogeneity is achieved, each flow fraction 7 possibly containing several elementary streams 6 represented as continuous lines in Figure 4. 5 The second embodiment is diagrammatically illustrated in figure 5, and also has about ten flow fractions 7, although the tie bricks are not shown in this figure. It may be advantageous for the said elements or tie 10 bricks 33 to be profiled so as to reduce the pressure loss of the said gas flow, while performing all other functions necessary to maintain a constant spacing between the said side walls 38, and to achieve or maintain the said predetermined degree of homogeneity 15 over the said cross-section S, for the said gas flow. Figures 7a to 7d are sectional views in the X-Z plane illustrating different profiles of tie beams or elements 33a, 33b, 33c, 33d, some (33c and 33d) being oblong shaped with a major axis 330 to facilitate 20 penetration of gas flow and reduce pressure losses (head losses) . The pressure loss P will normally be such that P 3 3 a > P33b > P33c and P33d. It may also be advantageous to use oblong shaped elements 33c, 33d in order to further reduce the 25 pressure loss, and to orient them as shown in figure 8 such that the orientation of the major axis 330 of the said tie bricks is parallel to the direction of the gas flow, particularly in the case in which the said sections are separated by walls 32 provided with 30 orifices or openings 320 through which the said gas flow can pass from one section to the next.

18 Example embodiment A furnace 1 of the type shown in Figure 1 was modeled and then built, comprising hollow walls as shown in Figures 4 and 4a according to the invention, 5 built with refractory bricks and tie bricks. Figure 4a is the construction drawing for the hollow wall 3, like any brick wall, the cross-hatched elements extending transversely (Y-Y' direction) over the entire width (0.5 m) of the said wall - this width including a 0.3 m 10 gas stream and 2 x 0.1 m hollow wall thicknesses. The scale in Figures 4 and 4a is given by L = 4.178 m, and by the thickness of each refractory brick = 91.5 mm. Before building this furnace, the gas flow streams inside the hollow walls were modeled by dividing the 15 total flow into about the fifty elementary flows or gas streams 6, the representation of a configuration according to the invention obtained by the said modeling was used to produce Figure 4 which shows the path of each gas stream 6. The said modeling was made 20 using computer means known in themselves. Figure 4 shows 3 zones denoted A, B and C, the gas flow circulating from left to right: - zone A corresponds to the formation of a gas flow with a cross-section S presenting the said degree of 25 homogeneity starting from a gas flow with cross section So << S, - zone B corresponds to an approximately tubular flow of the said gas flow, which has the said degree of homogeneity (with y = 0.25 over a length L' of the 30 wall, - zone C is the part in which the gas flow concentrates again, reducing from a cross-section S to a cross- 19 section So, at the passage through the wall between two successive sections. Advantages of the invention 5 The furnace according to the invention can actually solve the problem caused (either to maintain a constant quality of the carbonaceous blocks, or the energy consumption of the furnace, or the life of the furnace, in all these respects); this invention is an 10 improvement over existing furnaces made according to the state of the art. The energy consumption of the furnace is significantly reduced partly due to a better temperature homogeneity which prevents unnecessary 15 local overheating, and due to a lower pressure loss (see Figure 6a). The global gain, both in the energy consumption of the furnace and the consumption of refractory bricks, is at least 10% which is considerable in this type of 20 industry.

Claims

1. Ring furnace (1) with open type sections (2) for baking carbonaceous blocks (40) in a rotating fire comprising, along the longitudinal X direction of the furnace, a series of sections (2) separated by 5 headwalls (32) provided with openings (320), each section comprising, along the transverse Y direction of the furnace, hollow walls (3) through which a heating gas flow (35) comprising combustion gas or a cooling air flow (34) circulates, alternating with pits (4) 10 containing carbonaceous blocks (40) to be baked, each of the said hollow walls (3) in a section (2) being in communication with a wall in an upstream section and/or a wall in a downstream section, so as to form a conduit (5) through which the said gas flow (34, 35) circulates 15 from the upstream side to the downstream side, in the X longitudinal direction on all sections burned simultaneously in the said rotating fire, each of the said walls of a section comprising two vertical lateral partitions (38) in the X-Z plane, and elements in the 20 transverse Y direction for deflecting the said gas flow passing through the said wall and maintaining a constant spacing between the said lateral partitions (38), characterized in that each wall (3) comprises a means of maintaining, over at least one third of the 25 length L of said wall, a gas flow of rate D uniformly distributed over the entire normal cross-section S of the said wall in the Y-Z plane, with a degree of uniformity of the said flow distribution D defined by the expression "2 y D - 0.5 y D / y S", where "2 y D 30 0.5 y D" denotes the extent of the range of the flow of 21 rate D corresponding to a fraction y of the said normal cross-section S, and in which y is not more than 0.25.

2. Furnace according to claim 1, comprising sections separated by a headwall (32) with openings 5 with cross-section So (320) through which the said gas flow (34, 35) passes from one wall to the next wall, and in which the said wall comprises a means in its upstream part for obtaining a flow with cross-section S > So, starting from an initial flow of rate D with 10 cross-section So, with a degree of homogeneity equal to at least 0.50 D - 0.125 D / 0.25 S.

3. Furnace according to claim 2, in which the said means transforms a gas flow of rate D with an initial cross-section So at the upstream entry to the said 15 wall, into a flow with a cross-section S equal to at least 3.So and with the said degree of homogeneity, over a distance smaller than half the length L of the said wall.

4. Furnace according to claim 2, in which the said 20 means of obtaining the said gas flow of rate D with cross-section S and the said degree of homogeneity is composed of dividing elements or tie beams, dividing the said initial flow with cross-section So through a number of steps varying from 2 to 4. 25

5. Furnace according to claim 1 in which the said conduit has a constant cross-section, the said walls (32) having openings (320) with approximately the said cross-section S in the Y-Z plane, in order to form conduits (5) with an approximately constant cross 30 section S by a series of hollow walls (3) active simultaneously for the said fire, in which the said degree of homogeneity is achieved by a removable distribution means inserted on the upstream side of the 22 said rotating fire at the upstream end of the said conduit (5) in order to reinject the said gas flow into each conduit (5) with the said degree of homogeneity.

6. Furnace according to claim 5, in which the said 5 degree of homogeneity is also achieved using the said removable distribution means inserted on the downstream side of the said rotating fire, at the downstream end of the said conduit (5) formed by the series of hollow walls (3) active for the said fire, in order to suck up 10 the said gas flow without disturbing the said degree of homogeneity of the said gas flow on the upstream side.

7. Furnace according to any one of claims 5 and 6, in which the said distribution means is a containment or a parallelepiped shaped distribution panel (232) 15 with a plane horizontal section in the X-Y plane, chosen such that the said containment can be inserted vertically in the said shaft (37) of the said wall (3) or between two sections, and the said vertical plane cross-section in the Y-Z plane is slightly smaller than 20 the said cross-section S of the said wall in the Y-Z plane, with a surface parallel to the Y-Z plane provided with openings (2320) with a geometry calculated either to inject the said gas flow with the said degree of homogeneity on the upstream side of the 25 said conduit (5), or to suck up the said gas flows on the downstream side of the said conduit (5).

8. Furnace according to claims 1 to 7, in which the said means of maintaining a gas flow of rate D with the said degree of homogeneity over the said cross 30 section S comprises a number of elements or tie beams (33) fixed to the said lateral partitions (38) and uniformly distributed over the surface of the said lateral partitions (38) in the X-Z plane of the said 23 wall or the said conduit, with a sufficient number to ensure the said constant separation between the said lateral partitions (38) in order to divide the said gas flows into a number of flow fractions varying from 3 to 5 20, uniformly distributed over the entire cross-section S, and to ensure a flow with a predetermined orientation for the said fractions, and possibly along the said longitudinal direction X of the furnace.

9. Furnace according to either of claims 4 and 8, 10 in which the said elements or tie beams (33) are profiled so as to reduce the pressure loss in the said gas flow, while providing other required functions in order to maintain a constant separation between the said side walls (38) and to achieve or maintain the 15 said predetermined degree of homogeneity over the entire cross-section S, for the entire gas flow.